Southern and eastern sections of the Birmingham Box, along with the Birmingham-Nottingham Motorway, which falls short of the M1 by several miles, and limps there via the A42. Originally aiming at the A609/A6002 junction, this northern alignment was changed to a more southerly one that became the A42 to save money in the mid-70s.

The M42 includes a multiplex with the M6 Toll, one of only three multiplexes between two motorways in Great Britain.

Junctions

Catshill Interchange

The Catshill Interchange is a junction between the M5 and M42. For the M42, it forms the western terminus. The junction was originally a south-facing fork, only allowing access northbound M5 traffic to the M42, and forcing M42 traffic to take the M5 southbound. This design was because the M42 was originally planned to split into two further east, with the Lydiate Ash Link providing the missing movements.

Umberslade Interchange

The Umberslade Interchange is a triangular junction between M42 and M40 towards London. Priority is given betwen M40 and M42 westbound, with traffic wishing to remain on the M42 having to turn off. This junction would also have been the northern terminus of the unbuilt Strensham - Solihull Motorway.

Lydiate Ash Link

This was a different approach to north-facing slips to the M5. Rather than having them at Catshill Interchange, a longer link would cut the corner off. Plans to built this link lasted until the M5 was widened in the late 80s, when north-facing slips were added at Catshill.